Approach:
Escherichia coli O157:H7 and related STEC exist in two distinct biological compartments or ecological habitats. The primary STEC habitat is the nutrient-rich, homeothermic and generally hospitable, warm, moist gastrointestinal (GI) tract, while the secondary STEC habitat is the nutrient-poor, growth-limiting and thermally unstable external agricultural environment. Each of these compartments represents a unique ecological system, survival within which depends on the outcome of interactions between STEC and the other biotic and abiotic components. The fitness of STEC within each of these environments influences their ability to infect other animals, including humans, directly or through contamination of external materials. Understanding the key factors that influence the ability of STEC to survive and thrive under these disparate conditions is critical to rational design of intervention strategies to control these important zoonotic food-borne pathogens.
Intensive pre-harvest research efforts over the past decade have failed to identify any reliable evidence-based information or technology to significantly reduce STEC prevalence in livestock. Much recent evidence suggests that STEC are not only common but that they are essentially normal intestinal microflora of livestock. There is no historical scientific precedent for successful control or elimination of normal flora from any animal or plant species, so pre-harvest STEC control will be neither simple nor easy to achieve. The emphasis of past research efforts has been to look for modifiable risk factors (the epidemiologic approach) and to attempt intervention trials of naturally-infected or artificially-challenged animals, using fecal STEC O157 shedding as the primary outcome of interest. The role of the non-STEC indigenous microbial communities in both the primary STEC habitat (ruminant GI tract) and in the ambient agricultural environment (secondary STEC habitat) have been relatively unstudied. Furthermore, the STEC infected animal has been the intervention target of most pre-harvest STEC research over the past decade, while interventions targeting the secondary STEC habitat have been relatively ignored. Thus, to address these past research deficiencies, we have selected for emphasis in this proposal studies aimed at (1) understanding the interaction of STEC with the indigenous microbial communities in the primary and secondary habitat, and (2) interventions focusing on STEC reduction in the secondary STEC habitat.